The formation of effective adhesive bonds is critical in many applications, including the formation of a joint between two adherends. Fundamental to the formation of an effective bond is acceptance of the bonding material or adhesive by the articles to be joined, compatibility of the surface geometries, and environmental stability of the two sites where adhesion is to occur. In particular, the surface geometry must be such as to provide maximum wetted surface per unit area and interlocking features that result in a high strength bond-line.
While surface preparation or texturizing to achieve the foregoing characteristics is desired, prior art approaches for preparing adherends have not met this goal. For example, chemical cleansing and texturizing treatments preceding adhesive applications can easily result in surface and sub-surface contamination at the sites to be joined to thereby interfere with bonding. Further, with chemical as well as conventional laser beam treatments, surface textures are inadequately refined to efficiently interact with surface tension characteristics, wetability of adhesives, or to provide an optimum surface topography. Further, typical metal oxides formed on bonding surfaces generally are unstable and result in poor bond-line durability or fatigue life when used in a hostile environment as exemplified by hot-wet.
In view of the above considerations, it is apparent that a need is present for methodology that enhances adhesive bonding of two parts. Accordingly, it is a primary object of the present invention to provide a process for adhesively bonding two adherends to each other wherein a laser beam having free-electron laser characteristics aimed at surfaces to be adhered ablates organic and halogenated residues present on the surfaces.
Another object of the present invention is to provide a bonding process wherein such a laser beam aimed at surfaces to be adhered microtexturizes the surfaces by glazing the surfaces and forming a controlled stable oxide layer.
Yet another object of the present invention is to provide a process for adhesively bonding two adherends wherein such a laser beam aimed at surfaces to be adhered microtexturizes the surfaces to a controlled topography by forming depressions and whisker projections on the surfaces to enhance mechanical interlocking of the two adherends with the adhesive and substantially match surface tensions of the surfaces and the adhesive being used.
These and other objects of the invention will become apparent throughout the description thereof which now follows.